Note: Descriptions are shown in the official language in which they were submitted.
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NOVEL BICOMPONENT FIBERS HAVING DISTINCT
CRYSTALLINE AND AMORPHOUS POLYMER DOMAINS
AND METHODS OF MAKING THE SAME
FIELD OF INVENTION
The present invention relates generally to the field of synthetic
fibers. More particularly, the present invention relates to synthetic
bicomponent fibers having a sheath-core structure. In particularly
preferred forms, the present invention is embodied in multi-lobal
bicomponent fibers having a polyamide sheath entirely surrounding a core
formed of an amorphous polymer.
BACKGROUND AND SUMMARY OF THE INVENTION
Polyamide has been utilized extensively as a synthetic fiber. While
its structural and mechanical properties make it attractive for use in such
capacities as carpeting, it is nonetheless relatively expensive. It would
therefore be desirable to replace a portion of polyamide fibers with a core
formed from a relatively lower cost non-polyamide material. However,
replacing a portion of a 100% polyamide fiber with a core portion of a
relatively less expensive non-polyamide material may affect the
mechanical properties of the fiber to an extent that it would no longer be
useful in its intended end-use application (e.g., as a carpet fiber).
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Recently, U.S. Patent No. 5,549,957 has proposed multi-Ivbal
composite fibers having a nylon sheath and a core of a fiber-forming
polymer which can be, for example, "off spec" or reclaimed polymers.
(Column 4, lines 6-8.) The core can be polypropylene, polyethylene
terephthalate, high density polyethylene, polyester or polyvinyl chloride.
(Column 4, lines 17-20.) The core is covered with a sheath of virgin nylon
which constitutes between 30% to 50% by weight of the core/sheath fiber.
(Column 3, lines 65-67.)
1o Certain amorphous (non-crystalline) polymers, such as
polystyrene, represent attractive polymers due to their lower cost as
compared to virgin nylon. However, polystyrene is not considered to be a
fiber-forming polymer. A minor amount of polystyrene, however, has
been blended with an otherwise fiber-forming polymer (e.g., nylon or
~5 polypropylene) when forming electrically conductive sheath-core fibers
according to U.S. Patent No. 5,147,704.
Furthermore, U.S. Patent No. 3,718,534 to Okamoto et al disclose
that conjugate fibers may be formed from at least two different
2o fiber-forming polymers (see, column 6, lines 53-63), including polyamides,
and a so-called uniting constituent, including polystyrene, which is
exposed at the surface of the fiber so as to be easily dissolved by a
solvent. Dissolution of the uniting constituent thereby leaves the co-spun
fiber-forming constituents present in the final fiber product.
The presently known prior art therefore evidences the fact that
non-fiber-forming amorphous polymers, such as amorphous polystyrene,
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have not been employed as a structural component of finished
bicomponent synthetic fiber structures.
Broadly, the present invention relates to a bicomponent fiber
structure having a polyamide domain and another distinct cross-sectional
domain formed of an amorphous non-fiber-forming polymer. The
amorphous polymer domain is embedded entirely within, and thus
completely surrounded by, the polyamide domain. Preferably, the fibers
of this invention have a concentric sheath-core structure whereby the
1o polyamide domain forms the sheath and the amorphous non-fiber-forming
polymer forms the core. Surprisingly, even though the core is formed of a
non-fiber-forming amorphous polymer, the bicomponent sheath-core
fibers of this invention exhibit properties which are comparable in many
respects to fibers formed from 100% polyamide.
DETAILED DESCRIPTION OF THE PREFERRED
EXEMPLARY EMBODIMENTS
2o As used herein and in the accompanying claims, the term
°fiber-forming" is meant to refer to at least partly oriented, partly
crystalline, linear polymers which are capable of being formed into a fiber
structure having a length at least 100 times its width and capable of being
drawn without breakage at least about 10%. The term "non-fiber-forming"
is therefore meant to refer to amorphous (non-crystalline) linear polymers
which may be formed into a fiber structure, but which are incapable of
being drawn without breakage at least about 10%.
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The term "fiber" includes fibers of extreme or indefinite length
(filaments) and fibers of short length (staple). The term "yarn" refers to a
continuous strand or bundle of fibers.
The term "bicomponent fiber" is a fiber having at least two distinct
cross-sectional domains respectively formed of different polymers. The
term "bicomponent fiber" is thus intended to include concentric and
eccentric sheath-core fiber structures, symmetric and asymmetric
side-by-side fiber structures, island-in-sea fiber structures and pie wedge
fiber structures. Preferred according to the present invention are
concentric bicomponent sheath-core fiber structures having a polyamide
sheath and a non-fiber-forming amorphous polymer core, and thus the
disclosure which follows will be directed to such a preferred embodiment.
However, the present invention is equally applicable to other bicomponent
~5 fiber structures having a polyamide domain and a non-fiber-forming
amorphous polymer domain embedded entirely within, and thus
completely surrounded by, the polyamide domain.
The term "linear polymer" is meant to encompass polymers having
2o a straight chain structure wherein less than about 10% of the structural
units have side chains andlor branches.
The preferred polyamides useful to form the sheath of the
bicomponent fibers of this invention are those which are generically
25 known by the term "nylon" and are long chain synthetic polymers
containing amide (-CO-NH-) linkages along the main polymer chain.
Suitable melt spinnable, fiber-forming polyamides for the sheath of the
sheath-core bicomponent fibers according to this invention include those
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which are obtained by the polymerization of a lactam or an amino acid, or
those polymers formed by the condensation of a diamine and a
dicarboxylic acid. Typical polyamides useful in the present invention
include nylon 6, nylon 6I6, nylon 6I9, nylon 6/10, nylon 6T, nylon 6/12,
5 nylon 11, nylon 12, nylon 4,6 and copolymers thereof or mixtures thereof.
Polyamides can also be copolymers of nylon 6 or nylon 6/6 and a nylon
salt obtained by reacting a dicarboxylic acid component such as
terephthalic acid, isophthalic acid, adipic acid or sebacic acid with a
diamine such as hexamethylene diamine, methaxylene diamine, or 1,4-
bisaminomethylcyclohexane. Preferred are poly-e-caprolactam (nylon 6)
and polyhexamethylene adipamide (nylon 6/6). Most preferred is nylon 6.
Importantly, the core of the sheath-core fibers according to this
invention is formed of an amorphous linear polymer which in and of itself
~5 is non-fiber-forming. Suitable amorphous polymers for use in the practice
of this invention include polystyrene, polyisobutene and poly(methyl
methacrylate). Preferably, the core is formed of amorphous polystyrene,
with amorphous atactic polystyrene being particularly preferred.
2o The core will represent less than about 50% by weight of the fibers
according to this invention, with the sheath representing greater than
about 50 wt.%. More preferably, the core will be less than about 30 wt.%
of the fibers according to this invention, with the sheath being present in
the fibers in an amount greater than about 70 wt.%. Particular preferred
25 are fibers having a sheath of at least 75 wt.% nylon and a core of less
than about 25 wt.% amorphous non-fiber-forming polymer. Thus, weight
ratios of the sheath to the core in the fibers of this invention may range
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from about 1:1 to about 10:1, with a ratio of greater than about 2:1, and
more preferably greater than about 3:1 being preferred.
The sheath-core fibers are spun using conventional fiber-forming
equipment. Thus, for example, separate melt flows of the sheath and
core polymers may be fed to a conventional sheath-core spinnerette pack
such as those described in U.S. Patent Nos. 5,162,074, 5,125,818,
5,344,297 and 5,445,884 where the melt flows are
combined to form extruded multi-lobal (e.g., tri-, tetra-, yenta- or
to hexalobal) fibers having sheath and core structures. Preferably, the fibers
have a tri-lobal structure with a modification ratio of at least about 1.4,
more preferably between 2 and 4. In this regard, the term "modification
ratio" means the ratio R,/R2, where Rz is the radius of the largest circle
that is wholly within a transverse cross-section of the fiber, and R, is the
radius of the circle that circumscribes the transverse cross-section.
The extruded fibers are quenched, for example with air, in order to
solidify the fibers. The fibers may then be treated with a finish comprising
a lubricating oil or mixture of oils and antistatic agents. The thus formed
2 o fibers are then combined to form a yarn bundle which is then wound on a
suitable package.
In a subsequent step, the yarn is drawn and texturized to form a
bulked continuous fiber (BCF) yarn suitable for tufting into carpets. A
more preferred technique involves combining the extruded or as-spun
fibers into a yarn, then drawing, texturizing and winding into a package all
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in a single step. This one-step method of making BCF is generally known
in the art as spin-draw-texturing (SDT).
Nylon fibers for the purpose of carpet manufacturing have linear
densities in the range of about 3 to about 75 denier/filament (dpf)
(denier = weight in grams of a single fiber with a length of 9000 meters).
A more preferred range for carpet fibers is from about 15 to 25 dpf.
The BCF yarns can go through various processing steps well
known to those skilled in the art. For example, to produce carpets for
floor covering applications, the BCF yarns are generally tufted into a
pliable primary backing. Primary backing materials are generally selected
from woven jute, woven polypropylene, cellulosic nonwovens, and
nonwovens of nylon, polyester and polypropylene. The primary backing
~ 5 is then coated with a suitable latex material such as a conventional
styrene-butadiene (SB) latex, vinylidene chloride polymer, or vinyl
chloride-vinylidene chloride copolymers. It is common practice to use
fillers such as calcium carbonate to reduce latex costs. The final step is
to apply a secondary backing, generally a woven jute or woven synthetic
2o such as polypropylene. Preferably, carpets for floor covering applications
will include a woven polypropylene primary backing, a conventional SB
latex formulation, and either a woven jute or woven polypropylene
secondary carpet backing. The SB latex can include calcium carbonate
filler and/or one or more the hydrate materials listed above.
While the discussion above has emphasized the fibers of this
invention being formed into bulked continuous fibers for purposes of
making carpet fibers, the fibers of this invention can be processed to form
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fibers for a variety of textile applications. In this regard, the fibers can
be
crimped or otherwise texturized and then chopped to form random lengths
of staple fibers having individual fiber lengths varying from about 1'/Z to
about 8 inches.
The fibers of this invention can be dyed or colored utilizing
conventional fiber-coloring techniques. For example, the fibers of this
invention may be subjected to an acid dye bath to achieve desired fiber
coloration. Alternatively, the nylon sheath may be colored in the melt
prior to fiber-formation (i.e., solution dyed) using conventional pigments
for such purpose.
A further understanding of this invention will be obtained from the
following non-limiting Examples which illustrate specific embodiments
thereof.
EXAMPLES
Physical properties for the samples in the Examples below were
obtained using the following test procedures:
Measured Linear Density ~(denier~: The linear
density of the fibers was determined using
ASTM D1059, where the length of yarn used
was 90 cm.
$hrinkaae ~LAutoclave or Superba): Shrinkage
was computed using the linear densities before
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and after the autoclave or Superba heatsetting
of the yarn by the formula:
(datte~ dbetore)~datter
where dbero~e and dafte, are respectively the linear
densities before and after the autoclave or
Superba heatsetting.
Vetterman Drum Wear: The Vetterman Drum
test simulated wear according to ASTM D5417.
The degree of wear exhibit by the samples is
determined by a visual rating relative to
photographic standards of wear from The
Carpet and Rug Institute (CRI Reference Scale
available from CRI, P.O. Box 2048, Dalton,
Georgia, USA). Each of the common types of
carpet construction has a corresponding set of
photographic examples of unworn and worn
samples. The wear levels are from 5 to 1,
where 5 represents no visible wear and 1
2o represents considerable wear.
Boiling Water Shrinkage: Boiling water
shrinkage was determined using ASTM
D2259-1987.
file Height Retention: Pile height retention
was measured on trafficked carpet samples
using a compressometer manufactured by
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Schiefer having a 0.5 psi load and a 1 square
inch surface area pressure foot. The height of
the untrafficked carpet sample was first
measured at 12 locations within the carpet
5 sample using a template to ensure the sample
locates are measured after trafficking. The
samples rested for 24 hours after trafficking
and were then vacuumed. After resting an
additional 48 hours, the pile height of the
trafficked carpet sample was determined. The
average of the 12 final measurements was
divided by the average of the original 12
measurements and multiplied by 100 to give
the percent pile height retained. Testing and
~5 measurements were conducted at 70°F and
65% relative humidity.
Static Comra~ession: The static compression
was determined by testing four samples from
2o the material. Initial pile height of each carpet
sample was determined under a load of 0.5 psi
using the compressometer and methods as
described above in determining Pile Height
Retention. The Carpet was compressed for 24
25 hours under 50 psi. The compression force
was then removed and the carpet vacuumed
and allowed to recover with no loading for
another 24 hours, following which the final
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reading was done. The result was the average
for the four samples reported as a percent of
the original pile height. Testing and
measurements were conducted at 70°F and
65% relative humidity.
Example 1~comparative)
Nylon 6 (available from BASF Corp. as Ultramid~ BS-700F) was
extruded at 270°C into a modified trilobal cross section - 58 filaments
1100 denier to overall yarn. Winding speed was 2400 meters per minute.
Yarn was processed in a one step method in which the yarn is extruded,
drawn, and textured in a continuous process. Two of these yarns were
then combined in a cable twisting operation. The cabled yarn had a 3.75
twist per inch °S" twist. Skeins of the cabled yarn were heat set in an
~5 water autoclave using a temperature cycle of 270°F-230°F-
270°F-230°F-
270°F.
The yarn was then tufted on an 118th gauge carpet tufting machine
to a pile height of 9/16" and weight of 35 oz. of face fiber per square yard
20 of carpet. Carpet was then dyed to a light brown shade on a continuous
dye range. This carpet then had latex and a secondary backing applied.
The physical properties of the yarn and tufted carpet are noted
below in Table 1.
Example 2 ~(inventionl
The nylon 6 resin described in example 1 was extruded at 270°C.
Polystyrene (BASF PS2820 unfilled, nominal melt flow of 20 @200°C,
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5000g using ASTM D1238 - cond. G) was extruded at a polymer
temperature of 270°C. These polymers were combined in a sheath-core
bicomponent fiber spin pack. The polystyrene resin was channeled into
the core of 58 filaments using thin etched plates such as those described
in USP 5,344,297 to Hills and USP 5,445,884 to Hoyt et al .
The combined melt polymer flows were passed through the
same trilobal capillary and orifice as in example 1. Metering of the two
polymer flows was controlled to produce a 85:15 weight ratio of nylon 6
sheath to polystyrene core. The yarn was drawn and textured in a
continuous process, resulting in a 1100 denier 58 filament yarn. This yarn
was cabled and heat set (autoclaved) and tufted in to carpet as described
in Example 1. Physical properties of the yarn and carpet are noted below
in Table 1.
Example 3 (invention)
Example 2 was repeated except that the weight ratio of nylon 6 to
polystyrene was 80:20. The yarn of this Example 2 was cabled, heat set
(autoclaved) and tufted into carpet as described in Example 1. Physical
properties of the yarn and carpet are noted below in Table 1.
217
Example 4 (invention)
Example 2 was repeated, except that the weight ratio of nylon 6 to
polystyrene was 75:25. This yarn was cabled, heat set (autoclaved) and
tufted into carpet as described in Example 1. Physical properties of the
yarn and carpet are noted below in Table 1.
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Exam~l~,inventionl
Example 2 was repeated, except that the weight ratio of nylon 6 to
polystyrene was 70:30. This yarn was cabled, heat set (autoclaved) and
tufted into carpet as described in Example 1. Physical properties of the
yarn and carpet are noted below in Table 1.
Example 6 ~(comparativel
Nylon 6 (available from BASF Corp. as Ultramid~ BS-700F) was
extruded at 270°C into a modified trilobal cross section - 58 filaments
1300 denier to overall yarn. Winding speed was 2400 meters per minute.
Yarn was processed in a one step method in which the yarn is extruded,
drawn, and textured in a continuous process. Two ends of this yarns
were then combined in a cable twisting operation to obtain a cabled yarn
with 4.5 twists per "S" twist. This cabled yarn was heat set using steam in
~5 a Superba heat set tunnel at a 255°C process temperature.
The yarn was then tufted on an 118th gauge carpet tufting machine
into both 30 oz/sq. yard and 45 ozlsq. yd. carpets with pile heights of
9/l6ths and 11/16ths respectively.
Example 7 ~(Comparativel
Example 6 was repeated, except that the heat set yarns were
stuffer box textured before tufting into carpets.
Example 8 ~~Invention)
Example 6 was repeated except that the yarn was comprised of
sheath-core bicomponent fibers having a nylon sheath and a polystyrene
(BASF PS2820) core in a weight ratio of 75:25. The sheath-core
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bicomponent fibers were manufactured using the same yarn extrusion
process and equipment as in Examples 2-5.
Example 9~Inventionl
Example 8 was repeated, except that the heat set yarns were
stuffer box textured before tufting into carpets.
Examples 6-9 all formed carpets with no processing difficulties
noted for any of the yarns.
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TABLE 2
Exs. sn Exs. 8~9
Uncabled Single Yarn
Measured Linear Density (denier) 1344 1314
Elongation to Break (%) 36.7 44.8
Tenacity (g/denier) 2.65 2.27
Modulus @ 5% Extension (g/denier) 7.53 7.17
Cabled Unheatset Yarn
Denier (singles) 1358 1327
Denier (plied) 2720 2675
Heat set Untwisted Yarn
Measured Linear Density - singles
(denier)
(a) Straight Set 1698 1685
(b) Stuffer Box 1697 1601
Measured Linear Density - plied (denier)
(a) Straight Set 3452 3307
(b) Stuffer Box 3425 3171
Superba Shrinkage (%) - Singles
(a) Straight Set 0.20 0.21
(b) Stuffer Box 0.20 0.17
Superba Shrinkage (%) - Plied
(a) Straight Set 0.21 0.19
(b) Stuffer Box 0.20 0.16
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While the invention has been described in connection with what is
presently considered to be the most practical and preferred embodiment, it is
to
be understood that the invention is not to be limited to the disclosed
embodiment, but on the contrary, is intended to cover various modifications
and
equivalent arrangements included within the spirit and scope of the appended
claims.
